Electric heating device

ABSTRACT

An electric heating device in which a coil of corrugated metal ribbon forming the resistance element of the device is formed in a helix and mounted longitudinally in the bore of a tube of quartz, glass or the like, the helix being so wound that the undulations of the corrugations in adjacent loops of the ribbon are out of phase with each other to prevent telescoping of the adjacent loops. The metal of the resistance element has the characteristics of Kanthol and is an alloy containing iron, chromium, aluminum and tantalum. The metal is coated with an insulating film of oxide formed thereon by the heating of the helix in an oxidizing atmosphere while the corrugated metal ribbon is wound tightly around, and there restrained upon, a mandrel with The adjacent loops separated from each other. The heating in the oxidizing atmosphere leaves the film of insulating oxide film on the metal which electrically insulates adjacent loops from each other although in interengagement upon removal of the helix from the mandrel and the removal of the restraint on the helix. The heating also so anneals the metal ribbon that it resists the tendency to unwind from helix form and remains in the helical form.

United States Patent [72] Inventors Robert L. Arntz; FOREIGN PATENTS Rgmld Leger. both of Mansfield. Ohio 23,676 1 1 1915 0163: Britain 219 354 0 May 8 1969 Primary Examiner-.l. V. Truhe [45] Patented .Inly 2 1, 197! Assistant Examiner-Gale R. Peterson [73] Assign Dominion m Col-pond Altamey-Woodling, Krost, Granger & Rust Mamfield, Ohio [54] ELECTRIC HEATING DEVICE ABSTRACT: An electric heating device in which a coil of c0rrugated metal ribbon forming the resistance element of the device is formed in a helix and mounted longitudinally in the bore of a tube of quartz, glass or the like, the helix being so wound that the undulations of the corrugations in adjacent loops of the ribbon are out of phase with each other to prevent telescoping of the adjacent loops. The metal of the resistance element has the characteristics of Kanthol and is an alloy containing iron, chromium, aluminum and tantalum. The metal is coated with an insulating film of oxide formed thereon by the heating of the helix in an oxidizing atmosphere while the corrugated metal ribbon is wound tightly around, and there restrained upon, a mandrel with The adjacent loops separated from each other. The heating in the oxidizing atmosphere leaves the film of insulating oxide film onthe metal which electrically insulates adjacent loops from each other although in interengagement upon removal of the helix from the mandrel and the removal of the restraint on the helix. The heating also so anneals the metal ribbon that it resists the tendency to unwind from helix form and remains in the helical form.

PATENTEBJULZTIQ?! 3596,05?

By EON/4L0 E, LEGEE WM 7rd M ELECTRIC HEATING DEVICE Our invention relates to electric heating and to method of making the same.

An important application of our invention is in its use as a heating device for electric bread toasters, although it is of course useful in other applications as well. In a bread toaster, for example, two of the heating devices would be positioned in the housing of the toaster, one on each side of the slot in which the bread is located. Examples of the type of bread toasters in which out heating devices are particularly adaptable are shown in US. Pat. No. 3,347,l53 and No. 3,358,584, both of which are assigned to the assignee of this application.

An object of our invention is to provide a heating device of this general class which is more efficient in its heating functions, and to provide an economical and practical method of making the same.

Other objects and a fuller understanding of this invention may be had by referring to the following description and claims, taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a longitudinal sectional view of one of our heating devices mounted in a housing, such as a toaster housing;

FIG. 2 is an end view looking in the direction of line 2-2 of FIG. 1; and

FIG. 3 is an enlarged sectional view taken through the line 3-3 of FIG. 1.

The preferred form of our invention, as illustrated in the drawing, is mounted in a housing, such as a toaster housing, between two supporting walls 11. These supporting walls 11 are spaced apart as shown and have aligned flanged openings 12 provided therein for supporting the heating device.

Snugly fitting within the aligned flanged openings 12 are the opposite end portions of the tube 13. This tube 13 is preferably made of fused quartz and may be made of material known under the trademark of Vycor. The wall of the tube may be clear or translucent and is of a characteristic which readily transmits infrared rays therethrough, that is such as to permit heat energy to readily penetrate the wall.

Mounted longitudinally of tube 13 in the bore thereof is a heating element 14. The heating element 1 3 is such that upon the electrical energization thereof it emits infrared rays and thus generates heat energy.

The heating element 14 is made of a long strip of appropriate metal such as the metal alloy known as Kanthal." The metal is a stainless steel alloy and contains iron, chromium, cobalt, aluminum and preferably also includes tantalum. The long ribbon of metal is first corrugated to provide a series of evenly spaced undulations along its length which adds to the heating surface of the element. The corrugated ribbon of metal is wrapped tightly around a cylindrical mandrel of ceramic or other appropriate material which is both a good heat insulator and electrical insulator. The corrugated ribbon is wound tightly in a helical form around the mandrel and held tightly in such form with the adjacent loops of the helix spaced apart so as not to be in electrical contact with each other.

In the dimensioning of the mandrel to be used and in the wrapping of the corrugated ribbon about the mandrel the undulations of the corrugations are disposed such that they are out of phase with each other. The undulations are such that crests 15 are formed at spaced intervals around the circumference of the helix. In the asynchronous winding of the corrugated ribbon around the mandrel whereby the undulations are out of phase with each other the crests 15 of adjacent loops are not in longitudinal alignment with each other. This arrangement provides that tendency of the adjacent loops of the helix to telescope or nest is resisted by the crests 15 of the adjacent loops.

The ceramic mandrel with the corrugated ribbon tightly wrapped around it and with the adjacent loops spaced apart is then placed in an oxidizing atmosphere. This may be an oven containing oxygen or containing air with sufficient oxygen therein for the oxidizing. The ribbon is then heated to a relatively high degree by the passing of an electrical current therethrough. An alternative way could be to heat the assembly of ribbon on the mandrel by other well-known means.

The heating of the corrugated ribbon in the oxidizing atmosphere causes the metal to oxidize and particularly to form an oxide containing aluminum oxide fomting a coating or film on all surfaces of the ribbon. This coating or film of oxide and particularly of aluminum oxide derived from the alloy of the original metal ribbon provides an electrical insulation between adjacent loops of the helix. Although all surfaces of the ribbon tend to become oxidized, it is particularly important that the edge surfaces of adjacent loops facing each other have this coating or film of aluminum oxide thereon.

The heating of the metal ribbon also tends to anneal it and to cause it to continue to stay generally in the same helical form as when tightly wrapped around the mandrel. The tantalum in the alloy particularly is useful in causing the helix to stay in a wound helical form even when removed from constraint around the mandrel.

After the heating of the helical ribbon sufficiently long to cause the required oxide to form thereon and to cause the metal to set or stay in its thus-wound helical form it is removed from the mandrel and is then in a somewhat self-supporting condition although, when held in its opposite ends, it tends to droop or sag under its own weight.

The opposite ends of the helix are bent radially inward to form bent-in end portions 16. Secured by welding or other suitable means to these bent-in end portions 16 are terminal pin members 17 extending in opposite directions generally along the axis of the helix. The terminal pin members 17 as well as the element 14 are of course good electrical conductors.

Slidably mounted upon each pin member 17 is an insulating piece 18, preferably ceramic, of both electrical and heat insulating characteristics. These insulating pieces 18 have central openings 18A extending therethrough which receive in a loose sliding fit the respective pin members 17. The assembly of helix l4, insulating pieces 18, and pin members 17 is then slid through one end of a tube 13 in such manner that the pin members 17 extend outwardly at opposite ends of the tube 13. The insulating pieces 18 slide loosely within the opposite end portions of the tube 13 and support the pin members 17 therein generally axially of the tube 13. The ceramic pieces 18 are in a loose sliding fit within the tube 13 at its opposite ends.

Positioned at the opposite ends of the tube 13 and. outwardly of the ceramic pieces 18 are first leaf spring members 19. These leaf spring members 19 tend to bear against the outer ends of tube 13 and the outermost exposed surface of the pieces 18.

Second leaf spring members 20 which have their free ends bent over to form bent-over end portions 20A are then positioned outwardly of the first leaf spring members 19. The bent-over end portions 20A are welded or otherwise suitably secured to the respective pin members 17. The upper ends, that is the anchored ends of the two leaf springs members 19 and 20 are placed together and against bus bars 21 whereby electrical energy from the bus bars may pass through the second leaf spring members 20 to the pin members 17 and hence through the helical element 14.

These upper or anchored ends of the two leaf spring members are tightly held and secured in position by means of two insulating members 23 and 24. As seen in the drawing the members 23 and 24 have interfitting parts and have aligned openings through which extend mounting bolts 22 which in turn are secured to the supporting wall 11 of the toaster or other device. Thus the two spring members 19 and 20 are firmly supported at the opposite ends of the assembly of tube 13 and helical element 14. The resilient strength of the leaf spring member 19 is greater than that of the leaf spring member 20, that is it is relatively more rigid than is the leaf spring member 20. To some extent the leaf spring member 19 provides a backup spring or helper" to the more resilient and yieldable leaf spring member 20.

his therefore seen that the leaf spring member 19 at the opposite ends of the heating device aid in holding the tube 13 against longitudinal movement and also aid in holding the heating element within the tube as it is confined between the two spaced insulating pieces 18. Also the two springs provide a resiliently yieldable force tending to maintain the heli cal element 14 within the tube intermediate of the two pieces 18. The leaf spring members 20 being good electrical conductors conduct electric current from the bus bars 21 through the upper end of leaf spring members 19 and hence through the leaf spring members 20 to the pin members 17.

As the helical element 14 tends to droop or sag intermediate of its ends it tends to engage the bottom wall of the tube 13. The deleterious effect of this is minimized by the spaced crests 15 which touch the inner surface of the tube 13 at spaced intervals, such as seen in FIG. 3.

By means of the new construction shown and described and the unique method of making the same, we have provided a very important and useful means for the provision of heating devices, for a number of applications and particularly for such devices as electric bread toasters. I

The present disclosure includes that contained in the appended claims, as well as that of the foregoing description.

Although this invention has been described in its preferred fonn and preferred practice with a certain degree of particularity, it is understood that the present disclosure of the preferred form and preferred practice has been made only by way of example and that numerous changes in the details of construction and the combination and arrangement of parts and steps may be resorted to without departing from the spirit and the scope of the invention as hereinafter claimed.

What we claim is:

1. An electric heating device comprising the combination of a tubular member, a heating element disposed in the bore of said tubular member, said heating element being a helix of metal disposed longitudinally in said tubular member and adapted to produce infrared heat rays upon electrical energization thereof, said tubular member being adapted to transmit said infrared heat rays therethrough, said helix being loosely fitting in said tubular member and movable through the open ends thereof, a pair of electrical terminal members each electrically and mechanically connected to one of the opposite ends of the helix and disposed generally axially of the tubular member, said terminal members being longitudinally movable with said opposite ends of the helix, a pair of heat and electrical insulating members disposed in the tubular member at its said opposite ends, respectively, to block egress of the helix from said opposite ends, said insulating members slidably receiving said terminal members, respectively, to permit limited longitudinal movement thereof relative to the insulating members, a pair of first leaf spring members each having an anchored end portion and a free end portion, said free end being disposed to abut a said insulating member and biased to urge said abutted insulating member in a direction inwardly of the tubular member, said first leaf spring members confining said insulating members and the helix therebetween within said tubular member, a pair of second leaf spring members each having an anchored end portion and a free end portion, said free end portion being electrically and mechanically connected to said terminal members, respectively, said second leaf spring members being disposed and biased to urge said terminal and the ends of the helix connected thereto inwardly of the tubular member, anchoring means for anchoring the anchored ends of the first and second leaf spring members, and electrical connecting means for connecting the anchored ends of the second leaf spring members to a source of electrical energy whereby electrical current may be passed through the second leaf spring members, the terminal members and the said helix for electrical energization of the heating element.

2. An electric heating device as claimed in claim 1 and in which the anchored ends of the said leaf spring members are anchored together b said anchoring means and the res ective first and second lea spring members dtverge from eac other as they extend from said anchored ends, the resilient yieldability of said second leaf spring members being greater than that of the first leaf spring members to permit greater longitudinal movement of the terminal members than the longitudinal movement of the insulating members outwardly of the tubular member permitted by the first leaf spring members.

3. An electric heating device as claimed in claim 1 and in which the anchored ends of said leaf spring members are clamped together by said anchoring means and together held in electrical interconnection with a bus bar of said electrical connecting means.

4. An electric heating device comprising in combination a tubular member having the infrared transmitting characteristics of quartz and Vycor, a heating element disposed in and extending along the bore of said tubular member, said heating element being an electrical-conducting metal adapted to generate heat upon electrical energization thereof, said heating element being disposed in a helix and being composed of an alloy containing iron, chromium and aluminum, said heating element being coated with an oxide film formed thereon by the oxidization of said alloy, said oxide film providing electrical insulation between adjacent loops of said helix, electrical terminal members secured to said heating element adjacent to opposite ends, extending longitudinally of the heating element, and protruding from the opposite ends, respectively, of said tubular member for connection with electrical leads, heat and electrical insulating members disposed in said tubular member adjacent the opposite ends thereof, said insulating members accommodating said terminal members to permit the same to extend from said tubular member and providing stops retaining said element in and tubular member intermediate said insulating members, and including, at each end of the tubular member, mounting means including a first leaf spring member and a second leaf spring member held together at corresponding anchored end portions in electrical connection with electrical conductor means, said first leaf spring member having its free end portion positioned to abut against an end of said tubular member and the insulating member therein at said end to confine the insulating member in the tubular member to resist longitudinal movement of the tubular member toward the said first leaf spring member, said second leaf spring member having its free end portion secured to said terminal member at said end, said second leaf spring member being adapted to provide electrical connection between said electrical conductor means and the terminal member to which secured, said second leaf spring member being resiliently biased to urge said terminal member in sliding engagement with the insulating member longitudinally inwardly of the tubular member to restrain the said heating element within said tubular member. 

1. An electric heating device comprising the combination of a tubular member, a heating element disposed in the bore of said tubular member, said heating element being a helix of metal disposed longitudinally in said tubular member and adapted to produce infrared heat rays upon electrical energization thereof, said tubular member being adapted to transmit said infrared heat rays therethrough, said helix being loosely fitting in said tubular member and movable through the open ends thereof, a pair of electrical terminal members each electrically and mechanically connected to one of the opposite ends of the helix and disposed generally axially of the tubular member, said terminal members being longitudinally movable with said opposite ends of the helix, a pair of heat and electrical insulating members disposed in the tubular member at its said opposite ends, respectively, to block egress of the helix from said opposite ends, said insulating members slidably receiving said terminal members, respectively, to permit limited longitudinal movement thereof relative to the insulating members, a pair of first leaf spring members each having an anchored end portion and a free end portion, said free end being disposed to abut a said insulating member and biased to urge said abutted insulating member in a direction inwardly of the tubular member, said first leaf spring members confining said insulating members and the helix therebetween within said tubular member, a pair of second leaf spring members each having an anchored end portion and a free end portion, said free end portion being electrically and mechanically connected to said terminal members, respectively, said second leaf spring members being disposed and biased to urge said terminal and the ends of the helix connected thereto inwardly of the tubular member, anchoring means for anchoring the anchored ends of the first and second leaf spring members, and electrical connecting means for connecting the anchored ends of the second leaf spring members to a source of electrical energy whereby electrical current may be passed through the second leaf spring members, the terminal members and the said helix for electrical energization of the heating element.
 2. An electric heating device as claimed in claim 1 and in which the anchored ends of the said leaf spring members are anchored together by said anchoring means and the respective first and second leaf spring members diverge from each other as they extend from said anchored ends, the resilient yieldability of said second leaf spring members being greater than that of the first leaf spring members to permit greater longitudinal movement of the terminal members than the longitudinal movement of the insulating members outwardly of the tubular member permitted by the first leaf spring members.
 3. An electric heating device as claimed in claim 1 and in which the anchored ends of said leaf spring members are clamped together by said anchoring means and together held in electrical interconnection with a bus bar of said electrical connecting means.
 4. An electric heating device comprising in combination a tubular member having the infrared transmitting characteristics of quartz and Vycor, a heating element disposed in and extending along the bore of said tubular member, said heating element being an electrical-conducting metal adapted to generate heat upon electrical energization thereof, said heating element being disposed in a helix and being composed of an alloy containing iron, chromium and aluminum, said heating element being coated with an oxide film formed thereon by the oxidization of said alloy, said oxide film providing electrical insulation between adjacent loops of said helix, electrical terminal members secured to said heating element adjacent to opposite ends, extending longitudinally of the heating element, and protruding from the opposite ends, respeCtively, of said tubular member for connection with electrical leads, heat and electrical insulating members disposed in said tubular member adjacent the opposite ends thereof, said insulating members accommodating said terminal members to permit the same to extend from said tubular member and providing stops retaining said element in and tubular member intermediate said insulating members, and including, at each end of the tubular member, mounting means including a first leaf spring member and a second leaf spring member held together at corresponding anchored end portions in electrical connection with electrical conductor means, said first leaf spring member having its free end portion positioned to abut against an end of said tubular member and the insulating member therein at said end to confine the insulating member in the tubular member to resist longitudinal movement of the tubular member toward the said first leaf spring member, said second leaf spring member having its free end portion secured to said terminal member at said end, said second leaf spring member being adapted to provide electrical connection between said electrical conductor means and the terminal member to which secured, said second leaf spring member being resiliently biased to urge said terminal member in sliding engagement with the insulating member longitudinally inwardly of the tubular member to restrain the said heating element within said tubular member. 